Income taxes - Uncertain tax positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, January 1	$ 82	$ 82	$ 69
Additions based on tax positions related to the current year	3	3	3
Additions for tax positions of prior years	0	0	10
Reductions for tax positions of prior years	0	(3)	0
Balance, December 31	85	82	82
Interest expense recognized in the year ended December 31	(5)	(9)	(1)
Interest payable as of December 31	$ 15	$ 10	$ 3